Intra mode coding

ABSTRACT

A method of and an apparatus for controlling intra prediction for decoding of a video sequence are provided. The method includes determining a ratio of a width to a height of a coding unit, and based on the determined ratio being different than one, adding, to a table including intra prediction modes corresponding to intra prediction angles, first wide angles toward a bottom-left edge of the coding unit, second wide angles toward a top-right edge of the coding unit, and additional intra prediction modes respectively corresponding to the first wide angles and the second wide angles. The method further includes selecting, for decoding the video sequence, one of the intra prediction modes and the additional intra prediction modes added to the table.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.16/549,524, filed on Aug. 23, 2019, in the United States Patent andTrademark Office, which is a continuation application of U.S. patentapplication Ser. No. 16/198,951, filed on Nov. 23, 2018, in the UnitedStates Patent and Trademark Office, which claims priority from U.S.Provisional Patent Application No. 62/734,996, filed on Sep. 21, 2018,in the United States Patent and Trademark Office, which are incorporatedherein by reference in their entireties.

BACKGROUND 1. Field

Methods and apparatuses consistent with embodiments relate to videoprocessing, and more particularly, a method and an apparatus for intramode coding.

2. Description of Related Art

Intra prediction modes used in High Efficiency Video Coding (HEVC) areillustrated in FIG. 1. In HEVC, there is a total of 35 intra predictionmodes, among which mode 10 (101) is a horizontal mode, mode 26 (102) isa vertical mode, and mode 2 (103), mode 18 (104) and mode 34 (105) arediagonal modes. The intra prediction modes are signaled by three mostprobable modes (MPMs) and 32 remaining modes.

To code an intra mode, a most probable mode (MPM) list of size 3 isbuilt based on intra modes of the neighboring blocks. This MPM list willbe referred to as the MPM list or a primary MPM list. One MPM flag issignaled to indicate whether a current mode belongs to the MPM list. Ifthe MPM flag is true, an unary code is used to signal an MPM index. Ifthe MPM flag is false, a 5 bit fix length coding is used to signal theremaining modes.

A process of generating the MPM list generation is shown as follows.Here, leftIntraDir indicates a mode in a left block, and aboveIntraDirindicates a mode in an above block. If the left or above block iscurrently not available, leftIntraDir or aboveIntraDir is set to anindex DC IDX. In addition, variables “offset ” and “mod” are theconstant values, which are set to 29 and 32, respectively.

• If (leftIntraDir == aboveIntraDir && leftIntraDir > DC_IDX) ∘ MPM [0]= leftlntraDir; ∘ MPM [1] = ((leftIntraDir + offset) % mod) + 2; ∘ MPM[2] = ((leftIntraDir − 1) % mod) + 2; • Else if (leftIntraDir ==aboveIntraDir) ∘ MPM [0] = PLANAR_IDX; ∘ MPM [1] = DC_IDX; ∘ MPM [2] =VER_IDX; • Else if (leftIntraDir != aboveIntraDir) ∘ MPM [0] =leftIntraDir; ∘ MPM [1] = aboveIntraDir; ∘ If (leftIntraDir > 0 &&aboveIntraDir > 0) ▪ MPM [2] = PLANAR_IDX; ∘ Else ▪ MPM [2] =(leftIntraDir + aboveIntraDir) < 2 ? VER_IDX : DC_IDX;

SUMMARY

According to embodiments, a method of controlling intra prediction fordecoding of a video sequence is performed by at least one processor andincludes determining a ratio of a width to a height of a coding unit,and based on the determined ratio being different than one, adding, to atable including a plurality of intra prediction modes corresponding tointra prediction angles, first wide angles toward a bottom-left edge ofthe coding unit, second wide angles toward a top-right edge of thecoding unit, and additional intra prediction modes respectivelycorresponding to the first wide angles and the second wide angles. Themethod further includes selecting, for decoding the video sequence, oneof the plurality of intra prediction modes and the additional intraprediction modes added to the table.

According to embodiments, an apparatus for controlling intra predictionfor decoding of a video sequence includes at least one memory configuredto store computer program code, and at least one processor configured toaccess the at least one memory and operate according to the computerprogram code. The computer program code includes determining codeconfigured to cause the at least one processor to determine a ratio of awidth to a height of a coding unit, and adding code configured to causethe at least one processor to, based on the determined ratio beingdifferent than one, add, to a table including a plurality of intraprediction modes corresponding to intra prediction angles, first wideangles toward a bottom-left edge of the coding unit, second wide anglestoward a top-right edge of the coding unit, and additional intraprediction modes respectively corresponding to the first wide angles andthe second wide angles. The computer program code further includesselecting code configured to cause the at least one processor to select,for decoding the video sequence, one of the plurality of intraprediction modes and the additional intra prediction modes added to thetable.

According to embodiments, a non-transitory computer-readable storagemedium storing instructions that cause a processor to determine a ratioof a width to a height of a coding unit, and based on the determinedratio being different than one, add, to a table including a plurality ofintra prediction modes corresponding to intra prediction angles, firstwide angles toward a bottom-left edge of the coding unit, second wideangles toward a top-right edge of the coding unit, and additional intraprediction modes respectively corresponding to the first wide angles andthe second wide angles. The instructions further cause the processor toselect, for decoding a video sequence, one of the plurality of intraprediction modes and the additional intra prediction modes added to thetable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of intra prediction modes in HEVC.

FIG. 2 is a simplified block diagram of a communication system accordingto an embodiment.

FIG. 3 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment.

FIG. 4 is a functional block diagram of a video decoder according to anembodiment.

FIG. 5 is a functional block diagram of a video encoder according to anembodiment.

FIG. 6 is a diagram of intra prediction modes in Versatile Video Coding(VVC) Draft 2.

FIG. 7 is a flowchart illustrating a method of controlling intraprediction for decoding of a video sequence, according to an embodiment.

FIG. 8 is a simplified block diagram of an apparatus for controllingintra prediction for decoding of a video sequence, according to anembodiment.

FIG. 9 is a diagram of a computer system suitable for implementingembodiments.

DETAILED DESCRIPTION

FIG. 2 is a simplified block diagram of a communication system (200)according to an embodiment. The communication system (200) may includeat least two terminals (210-220) interconnected via a network (250). Forunidirectional transmission of data, a first terminal (210) may codevideo data at a local location for transmission to the other terminal(220) via the network (250). The second terminal (220) may receive thecoded video data of the other terminal from the network (250), decodethe coded data and display the recovered video data. Unidirectional datatransmission may be common in media serving applications and the like.

FIG. 2 illustrates a second pair of terminals (230, 240) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (230, 240) may code video data captured at a locallocation for transmission to the other terminal via the network (250).Each terminal (230, 240) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 2, the terminals (210-240) may be illustrated as servers,personal computers and smart phones but the principles of embodimentsare not so limited. Embodiments find application with laptop computers,tablet computers, media players and/or dedicated video conferencingequipment. The network (250) represents any number of networks thatconvey coded video data among the terminals (210-240), including forexample wireline and/or wireless communication networks. Thecommunication network (250) may exchange data in circuit-switched and/orpacket-switched channels. Representative networks includetelecommunications networks, local area networks, wide area networksand/or the Internet. For the purposes of the present discussion, thearchitecture and topology of the network (250) may be immaterial to theoperation of embodiments unless explained herein below.

FIG. 3 is a diagram of a placement of a video encoder and a videodecoder in a streaming environment, according to an embodiment. Thedisclosed subject matter can be equally applicable to other videoenabled applications, including, for example, video conferencing,digital TV, storing of compressed video on digital media including CD,DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating,for example, an uncompressed video sample stream (302). That samplestream (302), depicted as a bold line to emphasize a high data volumewhen compared to encoded video bitstreams, can be processed by anencoder (303) coupled to the camera (301). The encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (304), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (305) for future use. One or morestreaming clients (306, 308) can access the streaming server (305) toretrieve copies (307, 309) of the encoded video bitstream (304). Aclient (306) can include a video decoder (310) which decodes theincoming copy of the encoded video bitstream (307) and creates anoutgoing video sample stream (311) that can be rendered on a display(312) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (304, 307, 309) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as VVC. The disclosed subjectmatter may be used in the context of VVC.

FIG. 4 is a functional block diagram of a video decoder (310) accordingto an embodiment.

A receiver (410) may receive one or more codec video sequences to bedecoded by the decoder (310); in the same or an embodiment, one codedvideo sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (412), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (410) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (410) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween receiver (410) and entropy decoder/parser (420) (“parser”henceforth). When receiver (410) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (415) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (415) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (310) may include a parser (420) to reconstructsymbols (421) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(310), and potentially information to control a rendering device such asa display (312) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (420) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameters corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter (QP) values, motion vectors, and soforth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (415), so to create symbols(421). The parser (420) may receive encoded data, and selectively decodeparticular symbols (421). Further, the parser (420) may determinewhether the particular symbols (421) are to be provided to a MotionCompensation Prediction unit (453), a scaler/inverse transform unit(451), an Intra Prediction unit (452), or a loop filter unit (454).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder (310) can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). It can output blockscomprising sample values that can be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(456). The aggregator (455), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (452) has generatedto the output sample information as provided by the scaler/inversetransform unit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (421)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (454). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (454) as symbols (421) from theparser (420), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (454) can be a sample stream that canbe output to the render device (312) as well as stored in the referencepicture memory (456) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (420)), the current reference picture(456) can become part of the reference picture buffer (457), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (310) may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (410) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (310) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal-to-noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 is a functional block diagram of a video encoder (303) accordingto an embodiment.

The encoder (303) may receive video samples from a video source (301)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (303).

The video source (301) may provide the source video sequence to be codedby the encoder (303) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (301) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (301) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more samples depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focuses on samples.

According to an embodiment, the encoder (303) may code and compress thepictures of the source video sequence into a coded video sequence (543)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (550). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (550) as they may pertain to video encoder (303) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the art readilyrecognizes as a “coding loop.” As an oversimplified description, acoding loop can consist of the encoding part of an encoder (530)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (533) embedded in the encoder (303) that reconstructs thesymbols to create the sample data that a (remote) decoder also wouldcreate (as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (534). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder (310), which has already been described in detail abovein conjunction with FIG. 4. Briefly referring also to FIG. 4, however,as symbols are available and en/decoding of symbols to a coded videosequence by entropy coder (545) and parser (420) can be lossless, theentropy decoding parts of decoder (310), including channel (412),receiver (410), buffer (415), and parser (420) may not be fullyimplemented in local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. The description of encodertechnologies can be abbreviated as they are the inverse of thecomprehensively described decoder technologies. Only in certain areas amore detail description is required and provided below.

As part of its operation, the source coder (530) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (532) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (533) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (534). In this manner, the encoder (303) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new frame to be coded, the predictor (535)may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the video coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare it for transmission via acommunication channel (560), which may be a hardware/software link to astorage device that may store the encoded video data. The transmitter(540) may merge coded video data from the video coder (530) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the encoder (303). Duringcoding, the controller (550) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (303) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (303) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The video coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

FIG. 6 is a diagram of intra prediction modes in VVC Draft 2.

In VVC Draft 2, there is a total of 87 intra prediction modes as shownin FIG. 6, among which mode 18 (601) is a horizontal mode, mode 50 (602)is a vertical mode, and mode 2 (603), mode 34 (604) and mode 66 (605)are diagonal modes. Modes −1 to 10 and modes 67 to 76 are calledWide-Angle Intra Prediction (WAIP) modes.

Thirty-five HEVC intra prediction modes are included in VVC Draft 2, andmode numbers of these 35 HEVC modes are 0, 1, 2, 4, 6, 8, 10, 12, 14,16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50,52, 54, 56, 58, 60, 62, 64, and 66.

In VVC Draft 2, a size of an MPM list is still 3, and a MPM listgeneration process is the same as HEVC. A difference is that an “offset”is changed to 61, and a variable “mod” is changed to 64 because thereare 67 signaled modes in VVC Draft 2.

For mode coding, firstly, one MPM flag is signaled to indicate whether acurrent mode belongs to the MPM list. If the MPM flag is true, then atruncated unary code is used to signal an MPM index. If the MPM flag isfalse, then 6 bit fix length coding is used to signal remaining modes.

The following clause from VVC Draft 2 describes a luma intra mode codingprocess:

1. The neighbouring locations ( xNbA, yNbA ) and ( xNbB, yNbB ) are setequal to ( xPb − 1, yPb ) and ( xPb, yPb − 1 ), respectively. 2. For Xbeing replaced by either A or B, the variables candIntraPredModeX arederived as follows: - The availability derivation process for a block asspecified in clause 6.4.X [Ed. (BB): Neighbouring blocks availabilitychecking process tbd] is invoked with the location ( xCurr, yCurr ) setequal to ( xPb, yPb ) and the neighbouring location ( xNbY, yNbY ) setequal to ( xNbX, yNbX ) as inputs, and the output is assigned toavailableX. - The candidate intra prediction mode candIntraPredModeX isderived as follows:  - If one or more of the following conditions aretrue, candIntraPredModeX is set equal to INTRA_DC. - The variableavailableX is equal to FALSE. - CuPredMode[ xNbX ][ yNbX ] is not equalto MODE_INTRA. - X is equal to B and yPb − 1 is less than ( ( yPb >>CtbLog2SizeY ) << CtbLog2SizeY ).  - Otherwise, candIntraPredModeX isset equal to IntraPredModeY[ xNbX ][ yNbX ]. 3. The candModeList[ x ]with x = 0..2 is derived as follows: - If candIntraPredModeB is equal tocandIntraPredModeA, the following applies:  - If candIntraPredModeA isless than 2 (i.e., equal to INTRA_PLANAR or INTRA_DC), candModeList[ x ]with x = 0..2 is derived as follows: candModeList[ 0 ] = INTRA_PLANAR(8-1) candModeList[ 1 ] = INTRA_DC (8-2) candModeList[ 2 ] =INTRA_ANGULAR50 (8-3)  - Otherwise, candModeList[ x ] with x = 0..2 isderived as follows: candModeList[ 0 ] = candIntraPredModeA (8-4)candModeList[ 1 ] = 2 + ( ( candIntraPredModeA + 61 ) % 64 ) (8-5)candModeList[ 2 ] = 2 + ( ( candIntraPredModeA − 1 ) % 64 ) (8-6) -Otherwise (candIntraPredModeB is not equal to candIntraPredModeA), thefollowing applies:  - candModeList[ 0 ] and candModeList[ 1 ] arederived as follows: candModeList[ 0 ] = candIntraPredModeA (8-7)candModeList[ 1 ] = candIntraPredModeB (8-8)  - If neither ofcandModeList[ 0 ] and candModeList[ 1 ] is equal to INTRA_PLANAR,candModeList[ 2 ] is set equal to INTRA_PLANAR,  - Otherwise, if neitherof candModeList[ 0 ] and candModeList[ 1 ] is equal to INTRA_DC,candModeList[ 2 ] is set equal to INTRA_DC,  - Otherwise, candModeList[2 ] is set equal to INTRA_ANGULAR50. 4. IntraPredModeY[ xPb ][ yPb ] isderived by applying the following procedure: - If intra_luma_mpm_flag[xPb ][ yPb ] is equal to 1, the IntraPredModeY[ xPb ][ yPb ] is setequal to candModeList[ intra_luma_mpm_idx[ xPb ][ yPb ] ]. - Otherwise,IntraPredModeY[ xPb ][ yPb ] is derived by applying the followingordered steps:  1. The array candModeList[ x ], x = 0..2 is modified bythe following ordered steps:  i. When candModeList[ 0 ] is greater thancandModeList[ 1 ], both values are swapped as follows: ( candModeList[ 0], candModeList[ 1 ] ) = Swap( candModeList[ 0 ], candModeList[ 1 ] )(8-9)   ii. When candModeList[ 0 ] is greater than candModeList[ 2 ],both values are swapped as follows: ( candModeList[ 0 ], candModeList[ 2] ) = Swap( candModeList[ 0 ], candModeList[ 2 ] ) (8-10)  iii. WhencandModeList[ 1 ] is greater than candModeList[ 2 ], both values areswapped as follows: ( candModeList[ 1 ], candModeList[ 2 ] ) = Swap(candModeList[ 1 ], candModeList[ 2 ] ) (8-11)  2. IntraPredModeY[ xPb ][yPb ] is derived by the following ordered steps:  i. IntraPredModeY[ xPb][ yPb ] is set equal to intra_luma_mpm_remainder[ xPb ][ yPb ].   ii.For i equal to 0 to 2, inclusive, when IntraPredModeY[ xPb ][ yPb ] isgreater than or equal to candModeList[ i ], the value of IntraPredModeY[xPb ][ yPb ] is incremented by one. The variable IntraPredModeY[ x ][ y] with x = xPb..xPb + cbWidth − 1 and y = yPb..yPb + cbHeight − 1 is setto be equal to IntraPredModeY[ xPb ][ yPb ].

In the development of VVC Draft 2, an MPM list with a size of 6 wasproposed. Planar and DC modes are included in the MPM list. Twoneighboring modes, left and above modes, are used to generate aremaining 4 MPMs.

However, in VVC Draft 2, the number of the available intra predictionmodes is more than 67, which costs many bits to signal. There is astrong correlation between a current block and its neighboring blocks,which may be used to reduce the number of signaled intra predictionmodes for the current block.

Proposed methods below may be used separately or combined in any order.

In the description below, if one mode is not a planar or DC mode, or onemode is generating prediction samples according a given predictiondirection, such as intra prediction modes 2 to 76 and −1 to −10 asdefined in VVC Draft 2, this mode is called an angular mode.

In the description below, an allowed intra prediction mode (AIPM) set isdefined as one mode set with modes that can be used for intra predictionof a current block, and a disallowed intra prediction mode (DIPM) set isdefined as one mode set with modes that cannot be signaled or used forintra prediction of the current block.

Two variables are used in this document, offset and mod. The values ofthese two variables can have the following two sets:

-   -   1) offset=61, mod=64; or    -   2) offset=62, mod=65.

In an embodiment, there are two intra prediction mode sets for eachblock, which are an AIPM set and a DIPM set. For each block, modes inthese two mode sets may be different depending on coded information ofneighboring blocks and/or a current block, and may include but not belimited to intra prediction modes of neighboring blocks, intraprediction modes of current blocks, an aspect ratio, a coded block flag(CBF), primary and/or secondary transform types, neighboringreconstructed samples and so on.

In an embodiment, the modes in the AIPM set and the DIPM sets aredependent on the intra prediction modes of the neighboring blocks.

In an embodiment, neighboring modes are included in the AIPM set but notincluded in the DIPM set.

In an embodiment, blocks with a same aspect ratio or a same width and/orheight can have a different AIPM set and/or a different DIPM set.

In an embodiment, for each angular neighboring mode, denoted byang_mode, certain modes can be derived by the below equations 1 and 2,and the derived modes are included in the AIPM set but not included inthe DIPM set.

(ang_mode+offset−% mod+2  (Equation 1)

(ang_mode−1+diff) % mod+2  (Equation 2)

In Equations 1 and 2, diff is a variable, and is a positive integer orzero. In an example, diff can be any value equal to or less than 6. Inanother example, diff can be any value equal to or less than 3. In stillanother example, diff can be any value in set {0, 1, 2, 3, 5, 7}.

In an embodiment, to reduce the complexity of reconstructing the AIPMset, a number of derived modes are restricted by a threshold, denoted byThres. Thres can be any positive integer, such as 16, 32 or 48.

In an embodiment, the modes in the AIPM and DIPM sets are dependent onthe inter prediction modes of the neighboring blocks.

In an embodiment, the modes in the AIPM and DIPM sets are dependent onwhether the neighboring blocks are intra coded, or inter coded, or codedby an Intra Block Copy (IBC) mode, or coded by a MERGE mode, or coded bya SKIP mode, or coded by another coding mode.

In an embodiment, reconstructed pixels of neighboring blocks are used toderive allowed and non-allowed intra prediction mode sets.

In an embodiment, a gradient of neighboring reconstructed samples isused to derive the modes in the AIPM and DIPM sets. The gradient can becomputed by one of the following methods including, but not limited to:a first-order gradient method, a second-order gradient method, and abiconjugate gradient method.

In an embodiment, an edge detection method or an image feature detectionmethod can be used to derive the modes in the AIPM and DIPM sets. Theedge detection method includes, but is not limit to, one of a Sobeloperator, a Laplace operator, a Canny edge detector, a Kayyali operator,a SUSAN corner detector, and so on.

In an embodiment, the number of modes included in the AIPM and DIPM setsare predefined and fixed for all blocks.

In an embodiment, the number of modes included in the AIPM set isdenoted by S, and S is equal to M plus a power of two, forexample=M+2^(K), where M and K are positive integers, for example, M=6and K=5. M can be no larger than 7. Examples values include but are notlimited to 3, 4, 5, 6, and 7.

In an embodiment, a size of the AIPM set is denoted by S, and S is equalto M plus multiple levels of a power of two, for exampleS=M+2^(K)+2^(L), where M, K, and L are positive integers, for exampleM=6, K=4, L=5. M can be no larger than 7. Examples values include butare not limited to 3, 4, 5, 6, and 7.

In an embodiment, the number of modes included in the AIPM and DIPM setsare predefined and fixed for each block size, or each block aspectratio, or each block shape. However, the number of modes included in theAIPM and DIPM sets can be different for different block sizes, or adifferent block aspect ratio, or a different block shape.

In an embodiment, when the size of the AIPM set is S and the number ofderived intra prediction modes from neighboring modes are less than S,default modes are used to fill the AIPM set.

In an embodiment, all HEVC intra prediction modes are included in thedefault modes. In an example, S is equal to or larger than 35.

In an embodiment, all intra prediction modes associated with even modeindices are included in the default modes. In an example, S is equal toor larger than 35.

In an embodiment, angular modes associated with odd mode indices areincluded into default modes after HEVC intra prediction modes have beenincluded.

In an embodiment, when the size of the AIPM set is 38, the default modesare predefined as follows {0, 1, 2, 50, 18, 34, 66, 10, 26, 42, 58, 6,14, 22, 30, 38, 46, 54, 62, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44,48, 52, 56, 60, 64, 17, 19, 49}.

In an embodiment, when the size of the AIPM set is larger than 35, allHEVC intra prediction modes, or all intra prediction modes associatedwith even mode indices, or all intra prediction modes associated withodd mode indices, are always included in the AIPM set, but not includedin the DIPM set.

In an embodiment, for the AIPM set, it can be further split into twolists, a primary MPM list and a non-MPM list, and a size of the non-MPMlist is a power of 2.

In an embodiment, to code a mode in the AIPM set, firstly, one MPM flagis signaled to indicate whether the current mode belongs to the primaryMPM list. If the MPM flag is true, a truncated unary code is used tosignal the MPM index. Otherwise, fix length coding is used to signal themode in the non-MPM list.

Twenty-eight or thirty wide angles and respective wide angular intraprediction modes are added into a table of original angles andrespective original angular intra prediction modes, according to anaspect ratio of a current block.

In an embodiment, 14 or 15 wide angles and respective wide angular intraprediction modes are added into a bottom-left direction of the currentblock (e.g., a bottom edge 606 of FIG. 6), and another 14 or 15 wideangles and respective wide angular intra prediction modes are added intoa top-right direction (e.g., a right edge 607 of FIG. 6) of the currentblock. Implementations of examples are shown in Tables 1-2 below.

An angle table for wide angles together with original angles are shownas follows.

In an example, an angle table of 32 angles (angTable[32]) may includeangles {0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 23, 26, 29, 32, 35,39, 45, 51, 57, 64, 73, 86, 102, 128, 171, 256, 341, 512, 1024}, inwhich angles {0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 23, 26, 29,32} are original angles and angles {35, 39, 45, 51, 57, 64, 73, 86, 102,128, 171, 256, 341, 512, 1024} are wide angles.

In other words, each of the angles may have an angular direction a withtan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32, 8/32, 10/32, 12/32,14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32, 32/32, 35/32, 39/32,45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32,256/32, 341/32, 512/32, 1024/32}.

Table 1 may be an example of such an angle table with respective intraprediction modes in VVC having 67 original angles and 67 respectiveoriginal angular intra prediction modes, to which 30 wide angles and 30respective wide angular intra prediction modes are added:

TABLE 1 Specification of intraPredAngle predModeIntra −15 −14 −13 −12−11 intraPredAngle 1024 512 341 256 171 predModeIntra −10 −9 −8 −7 −6 −5−4 −3 −2 −1 2 3 4 5 6 7 8 intraPredAngle 128 102 86 73 64 57 51 45 39 3532 29 26 23 20 18 16 predModeIntra 9 10 11 12 13 14 15 16 17 18 19 20 2122 23 24 25 intraPredAngle 14 12 10 8 6 4 3 2 1 0 −1 −2 −3 −4 −6 −8 −10predModeIntra 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42intraPredAngle −12 −14 −16 −18 −20 −23 −26 −29 −32 −29 −26 −23 −20 −18−16 −14 −12 predModeIntra 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5758 59 intraPredAngle −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6 8 10 12 14predModeIntra 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76intraPredAngle 16 18 20 23 26 29 32 35 39 45 51 57 64 73 86 102 128predModeIntra 77 78 79 80 81 intraPredAngle 171 256 341 512 1024

predModeIntra denotes intra prediction modes in VVC, and intraPredAngledenotes intra prediction angles.

In another example, an angle table of 31 angles (angTable[31]) mayinclude angles {0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 23, 26, 29,32, 35, 39, 45, 51, 57, 64, 73, 86, 102, 128, 171, 256, 341, 512}, inwhich angles {0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 23, 26, 29,32} are original angles and angles {35, 39, 45, 51, 57, 64, 73, 86, 102,128, 171, 256, 341, 512} are wide angles.

In other words, each of the angles may have an angular direction α withtan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32, 8/32, 10/32, 12/32,14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32, 32/32, 35/32, 39/32,45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32,256/32, 341/32, 512/32}.

Table 2 may be an example of such an angle table with respective intraprediction modes in VVC having 67 original angles and 67 respectiveoriginal angular intra prediction modes, to which 28 wide angles and 28respective wide angular intra prediction modes are added:

TABLE 2 Specification of intraPredAngle predModeIntra −14 −13 −12 −11intraPredAngle 512 341 256 171 predModeIntra −10 −9 −8 −7 −6 −5 −4 −3 −2−1 2 3 4 5 6 7 8 intraPredAngle 128 102 86 73 64 57 51 45 39 35 32 29 2623 20 18 16 predModeIntra 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 2425 intraPredAngle 14 12 10 8 6 4 3 2 1 0 −1 −2 −3 −4 −6 −8 −10predModeIntra 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42intraPredAngle −12 −14 −16 −18 −20 −23 −26 −29 −32 −29 −26 −23 −20 −18−16 −14 −12 predModeIntra 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5758 59 intraPredAngle −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6 8 10 12 14predModeIntra 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76intraPredAngle 16 18 20 23 26 29 32 35 39 45 51 57 64 73 86 102 128predModeIntra 77 78 79 80 intraPredAngle 171 256 341 512

The following text describes text changes (with strikethrough andunderlining) to VVC Draft 2, using the above-discussed embodiments:

8.2.4.2.7 Specification of INTRA_ANGULAR2..INTRA_ANGULAR66 intraprediction modes Inputs to this process are: -  the intra predictionmode predModeIntra, -  the neighbouring samples p[ x ][ y ], with x =−1, y = −1.refH − 1 and x = 0..refW − 1, y = −1, -  a variable nTbWspecifying the transform block width, -  a variable nTbH specifying thetransform block height, -  a variable refW specifying the referencesamples width, -  a variable refH specifying the reference samplesheight. Outputs of this process are the modified intra prediction ModepredModeIntra and the predicted samples predSamples[ x ][ y ], with x =0..nTbW + 1, y = 0..nTbH + 1. The variable whRatio is set equal to min(abs( Log2( nTbW / nTbH ) ), 2 ). For non-square blocks (nTbW is notequal to nTbH), the intra prediction mode predModeIntra is modified asfollows: - If all of the following conditions are true, predModeIntra isset equal to ( predModeIntra + 65 ). - nTbW is greater than nTbH -predModeIntra is greater than or equal to 2 - predModeIntra is less than( whRatio > 1 ) ? 12 : 8 - Otherwise, if all of the following conditionsare true, predModelntra is set equal to ( predModelntra − 67 ). - nTbHis greater than nTbW - predModeIntra is less than or equal to 66predModeIntra is greater than ( whRatio > 1 ) ? 56 : 60

Table 8-5 specifies the mapping table between predModelntra and theangle parameter intraPredAngle and FIG. 8-3 illustrates the intraprediction angles for each angle parameter.

TABLE 8-5 Specification of intraPredAngle predModelntra −14 −13 −12 −11intraPredAngle 512 341 256 171 predModeIntra −10 −9 −8 −7 −6 −5 −4 −3 −2−1 2 3 4 5 6 7 8 intraPredAngle 128 102 86 73 64 57 51 45 39 35 32 29 2623 20 18 16 predModeIntra 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 2425 intraPredAngle 14 12 10 8 6 4 3 2 1 0 −1 −2 −3 −4 −6 −8 −10predModeIntra 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42intraPredAngle −12 −14 −16 −18 −20 −23 −26 −29 −32 −29 −26 −23 −20 −18−16 −14 −12 predModeIntra 43 44 45 46 47 48 49 50 51 52 53 54 55 56 5758 59 intraPredAngle −10 −8 −6 −4 −3 −2 −1 0 1 2 3 4 6 8 40 12 14predModeIntra 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76intraPredAngle 16 18 20 23 26 29 32 35 39 45 51 57 64 73 86 102 128predModeIntra 77 78 79 80 intraPredAngle 171 256 341 512

TABLE 9-4 Syntax elements and associated binarizations multi_type_tree() mtt_split_cu_flag FL cMax = 1 mtt_split_cu_vertical_flag FL cMax = 1mtt_split_cu_binary_flag FL cMax = 1 coding_unit( ) cu_skip_flag[ ][ ]FL cMax = 1 pred_mode_flag FL cMax = 1 intra_luma_mpm_flag[ ][ ] FL cMax= 1 intra_luma_mpm_idx[ ][ ] TR cMax = 2, cRiceParam = 0intra_luma_mpm_remainder[ ][ ] FL cMax = 31 

intra_chroma_pred_mode[ ][ ] 9.3.3.6 — merge_affine flag[ ][ ] FL cMax =1 merge_flag[ ][ ] FL cMax = 1 merge_idx[ ][ ] TR cMax = MaxNumMergeCand− 1, cRiceParam = 0 inter_pred_idc[ x0 ][ y0 ] 9.3.3.7 —inter_affine_flag[ ][ ] FL cMax = 1 cu_affine_type_flag[ ][ ] FL cMax =1 ref_idx_l0[ ][ ] TR cMax = num_ref_idx_l0_active minus1, cRiceParam =0 mvp_l0_flag[ ][ ] FL cMax = 1 ref_idx_l1[ ][ ] TR cMax =num_ref_idx_l1_active minus1, cRiceParam = 0 mvp_l1_flag[ ][ ] FL cMax =1 amvr_mode[ ][ ] TR cMax = 2, cRiceParam = 0 cu_cbf FL cMax = 1

FIG. 7 is a flowchart illustrating a method (700) of controlling intraprediction for decoding of a video sequence, according to an embodiment.In some implementations, one or more process blocks of FIG. 7 may beperformed by the decoder (310). In some implementations, one or moreprocess blocks of FIG. 7 may be performed by another device or a groupof devices separate from or including the decoder (310), such as theencoder (303).

Referring to FIG. 7, in a first block (710), the method (700) includesdetermining a ratio of a width to a height of a coding unit.

In a second block (720), the method (700) includes, based on thedetermined ratio being different than one, adding, to a table includinga plurality of intra prediction modes corresponding to intra predictionangles, first wide angles toward a bottom-left edge of the coding unit,second wide angles toward a top-right edge of the coding unit, andadditional intra prediction modes respectively corresponding to thefirst wide angles and the second wide angles.

A number of the first wide angles added to the table may be 14. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the first wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32}.

A number of the second wide angles added to the table may be 14. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the second wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32}.

A number of the first wide angles added to the table may be 15. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the first wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32, 1024/32}.

A number of the second wide angles added to the table may be 15. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the second wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32, 1024/32}.

A first number of the plurality of intra prediction modes included inthe table may be 67, a second number of the additional intra predictionmodes added to the table may be 28, and the table may include Table 2above.

In a third block (730), the method (700) includes selecting, fordecoding the video sequence, one of the plurality of intra predictionmodes and the additional intra prediction modes added to the table.

Although FIG. 7 shows example blocks of the method (700), in someimplementations, the method (700) may include additional blocks, fewerblocks, different blocks, or differently arranged blocks than thosedepicted in FIG. 7. Additionally, or alternatively, two or more of theblocks of the method (700) may be performed in parallel.

Further, the proposed methods may be implemented by processing circuitry(e.g., one or more processors or one or more integrated circuits). In anexample, the one or more processors execute a program that is stored ina non-transitory computer-readable medium to perform one or more of theproposed methods.

FIG. 8 is a simplified block diagram of an apparatus (800) forcontrolling intra prediction for decoding of a video sequence, accordingto an embodiment.

Referring to FIG. 8, the apparatus (800) includes determining code(810), adding code (820), and selecting code (830).

The determining code (810) is configured to determine a ratio of a widthto a height of a coding unit.

The adding code (820) is configured to, based on the determined ratiobeing different than one, add, to a table including a plurality of intraprediction modes corresponding to intra prediction angles, first wideangles toward a bottom-left edge of the coding unit, second wide anglestoward a top-right edge of the coding unit, and additional intraprediction modes respectively corresponding to the first wide angles andthe second wide angles.

A number of the first wide angles added to the table may be 14. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the first wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32}.

A number of the second wide angles added to the table may be 14. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the second wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32}.

A number of the first wide angles added to the table may be 15. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the first wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32, 1024/32}.

A number of the second wide angles added to the table may be 15. Each ofthe intra prediction angles included in the table may have an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}, and each of the second wide angles added to the table may havethe angular direction a with tan(α) equal to {35/32, 39/32, 45/32,51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32,341/32, 512/32, 1024/32}.

A first number of the plurality of intra prediction modes included inthe table may be 67, a second number of the additional intra predictionmodes added to the table may be 28, and the table may include Table 2above.

The selecting code (830) is configured to select, for decoding the videosequence, one of the plurality of intra prediction modes and theadditional intra prediction modes added to the table.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media.

FIG. 9 is a diagram of a computer system (900) suitable for implementingembodiments.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 9 for computer system (900) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments. Neither should the configuration of components beinterpreted as having any dependency or requirement relating to any oneor combination of components illustrated in the exemplary embodiment ofa computer system (900).

Computer system (900) may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (901), mouse (902), trackpad (903), touchscreen (910), data-glove (904), joystick (905), microphone (906),scanner (907), camera (908).

Computer system (900) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (910), data-glove (904), or joystick (905), but there canalso be tactile feedback devices that do not serve as input devices),audio output devices (such as: speakers (909), headphones (notdepicted)), visual output devices (such as screens (910) to includecathode ray tube (CRT) screens, liquid-crystal display (LCD) screens,plasma screens, organic light-emitting diode (OLED) screens, each withor without touch-screen input capability, each with or without tactilefeedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (900) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(920) with CD/DVD or the like media (921), thumb-drive (922), removablehard drive or solid state drive (923), legacy magnetic media such astape and floppy disc (not depicted), specialized ROM/ASIC/PLD baseddevices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (900) can also include interface(s) to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include global systems for mobile communications(GSM), third generation (3G), fourth generation (4G), fifth generation(5G), Long-Term Evolution (LTE), and the like, TV wireline or wirelesswide area digital networks to include cable TV, satellite TV, andterrestrial broadcast TV, vehicular and industrial to include CANBus,and so forth. Certain networks commonly require external networkinterface adapters that attached to certain general purpose data portsor peripheral buses ((949)) (such as, for example universal serial bus(USB) ports of the computer system (900); others are commonly integratedinto the core of the computer system (900) by attachment to a system busas described below (for example Ethernet interface into a PC computersystem or cellular network interface into a smartphone computer system).Using any of these networks, computer system (900) can communicate withother entities. Such communication can be uni-directional, receive only(for example, broadcast TV), uni-directional send-only (for exampleCANbus to certain CANbus devices), or bi-directional, for example toother computer systems using local or wide area digital networks.Certain protocols and protocol stacks can be used on each of thosenetworks and network interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (940) of thecomputer system (900).

The core (940) can include one or more Central Processing Units (CPU)(941), Graphics Processing Units (GPU) (942), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(943), hardware accelerators (944) for certain tasks, and so forth.These devices, along with Read-only memory (ROM) (945), Random-accessmemory (RAM) (946), internal mass storage such as internal non-useraccessible hard drives, solid-state drives (SSDs), and the like (947),may be connected through a system bus (948). In some computer systems,the system bus (948) can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus (948), or through a peripheral bus (949).Architectures for a peripheral bus include peripheral componentinterconnect (PCI), USB, and the like.

CPUs (941), GPUs (942), FPGAs (943), and accelerators (944) can executecertain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(945) or RAM (946). Transitional data can also be stored in RAM (946),whereas permanent data can be stored for example, in the internal massstorage (947). Fast storage and retrieve to any of the memory devicescan be enabled through the use of cache memory, that can be closelyassociated with one or more CPU (941), GPU (942), mass storage (947),ROM (945), RAM (946), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of embodiments, or they can be of the kind well known andavailable to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (900), and specifically the core (940) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (940) that are of non-transitorynature, such as core-internal mass storage (947) or ROM (945). Thesoftware implementing various embodiments can be stored in such devicesand executed by core (940). A computer-readable medium can include oneor more memory devices or chips, according to particular needs. Thesoftware can cause the core (940) and specifically the processorstherein (including CPU, GPU, FPGA, and the like) to execute particularprocesses or particular parts of particular processes described herein,including defining data structures stored in RAM (946) and modifyingsuch data structures according to the processes defined by the software.In addition or as an alternative, the computer system can providefunctionality as a result of logic hardwired or otherwise embodied in acircuit (for example: accelerator (944)), which can operate in place ofor together with software to execute particular processes or particularparts of particular processes described herein. Reference to softwarecan encompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. Embodiments encompass anysuitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

1. A method of controlling intra prediction for decoding of a videosequence, the method being performed by at least one processor, and themethod comprising: determining a ratio of a width to a height of acoding unit; based on the determined ratio being different than one,adding, to a table including a plurality of intra prediction modescorresponding to intra prediction angles, first wide angles toward abottom-left edge of the coding unit, second wide angles toward atop-right edge of the coding unit, and additional intra prediction modesrespectively corresponding to the first wide angles and the second wideangles; and selecting, for decoding the video sequence, one of theplurality of intra prediction modes and the additional intra predictionmodes added to the table.
 2. The method of claim 1, wherein a number ofthe first wide angles added to the table is
 14. 3. The method of claim2, wherein each of the first wide angles added to the table has anangular direction a with tan(α) equal to {35/32, 39/32, 45/32, 51/32,57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32, 256/32, 341/32,512/32}.
 4. The method of claim 1, wherein a number of the second wideangles added to the table is
 14. 5. The method of claim 4, wherein eachof the second wide angles added to the table has an angular direction awith tan(α) equal to {35/32, 39/32, 45/32, 51/32, 57/32, 64/32, 73/32,86/32, 102/32, 128/32, 171/32, 256/32, 341/32, 512/32}.
 6. The method ofclaim 1, wherein a number of the first wide angles added to the table is15.
 7. The method of claim 6, wherein each of the first wide anglesadded to the table has an angular direction a with tan(α) equal to{35/32, 39/32, 45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32,171/32, 256/32, 341/32, 512/32, 1024/32}.
 8. The method of claim 1,wherein a number of the second wide angles added to the table is
 15. 9.The method of claim 8, wherein each of the second wide angles added tothe table has an angular direction a with tan(α) equal to {35/32, 39/32,45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32,256/32, 341/32, 512/32, 1024/32}.
 10. The method of claim 1, whereineach of the intra prediction angles included in the table has an angulardirection a with tan(α) equal to {0/32, 1/32, 2/32, 3/32, 4/32, 6/32,8/32, 10/32, 12/32, 14/32, 16/32, 18/32, 20/32, 23/32, 26/32, 29/32,32/32}.
 11. An apparatus for controlling intra prediction for decodingof a video sequence, the apparatus comprising: at least one memoryconfigured to store computer program code; and at least one processorconfigured to access the at least one memory and operate according tothe computer program code, the computer program code comprising:determining code configured to cause the at least one processor todetermine a ratio of a width to a height of a coding unit; adding codeconfigured to cause the at least one processor to, based on thedetermined ratio being different than one, add, to a table including aplurality of intra prediction modes corresponding to intra predictionangles, first wide angles toward a bottom-left edge of the coding unit,second wide angles toward a top-right edge of the coding unit, andadditional intra prediction modes respectively corresponding to thefirst wide angles and the second wide angles; and selecting codeconfigured to cause the at least one processor to select, for decodingthe video sequence, one of the plurality of intra prediction modes andthe additional intra prediction modes added to the table.
 12. Theapparatus of claim 11, wherein a number of the first wide angles addedto the table is
 14. 13. The apparatus of claim 12, wherein each of thefirst wide angles added to the table has an angular direction a withtan(α) equal to {35/32, 39/32, 45/32, 51/32, 57/32, 64/32, 73/32, 86/32,102/32, 128/32, 171/32, 256/32, 341/32, 512/32}.
 14. The apparatus ofclaim 11, wherein a number of the second wide angles added to the tableis
 14. 15. The apparatus of claim 14, wherein each of the second wideangles added to the table has an angular direction a with tan(α) equalto {35/32, 39/32, 45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32,128/32, 171/32, 256/32, 341/32, 512/32}.
 16. The apparatus of claim 11,wherein a number of the first wide angles added to the table is
 15. 17.The apparatus of claim 16, wherein each of the first wide angles addedto the table has an angular direction a with tan(α) equal to {35/32,39/32, 45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32,256/32, 341/32, 512/32, 1024/32}.
 18. The apparatus of claim 11, whereina number of the second wide angles added to the table is
 15. 19. Theapparatus of claim 18, wherein each of the second wide angles added tothe table has an angular direction a with tan(α) equal to {35/32, 39/32,45/32, 51/32, 57/32, 64/32, 73/32, 86/32, 102/32, 128/32, 171/32,256/32, 341/32, 512/32, 1024/32}.
 20. A non-transitory computer-readablestorage medium storing instructions that cause a processor to: determinea ratio of a width to a height of a coding unit; based on the determinedratio being different than one, add, to a table including a plurality ofintra prediction modes corresponding to intra prediction angles, firstwide angles toward a bottom-left edge of the coding unit, second wideangles toward a top-right edge of the coding unit, and additional intraprediction modes respectively corresponding to the first wide angles andthe second wide angles; and select, for decoding a video sequence, oneof the plurality of intra prediction modes and the additional intraprediction modes added to the table.